20     THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ IV, I.

veins. Fairley and Mackie found in goats, infected heavily with cercariae of
S. spindalis, an overflow distribution of schistosomes in atypical situations
in the early phases of the disease, and later a biological equilibrium became estab-
lished between the worms and the definitive hosts, when the worms limit themselves
to their ordinary habitat, viz., the portal and mesenteric veins. They also say
that the distribution of S. spindalis, within the blood vascular system, corresponds
to S. mansoni and S. japonicum than to S. haematobium. The experimental
infection in calves here, with massive doses of cercariae of S. spindalis, failed to
produce nasal schistosomiasis, in other words, it means that S . spindalis does not
inhabit and develop in the nasal veins, and the adult worms are found only in the
portal and mesenteric veins, consequently the ova are voided only with the faeces
of the host. As regards the nasal schistosome, the author has not been able to
obtain any in the portal or mesenteric veins of animals examined in the abattoir
or in the calves experimentally infected with nasal schistosomiasis. The absence
of these in the portal system and the absence of their ova in the faeces or urine
of the animals having nasal schistosomiasis at once suggests that these parasites
do not develop in the portal or mesenteric veins. The ova of S. spindalis, on the
other hand, have not been met with in the nasal discharge. It would therefore
appear that the nasal schistosomes choose the nasal veins only as their habitat
and develop there, and S. spindalis inhabits only the portal and mesenteric veins.

It would be interesting to note here the findings in two guinea-pigs, one
infected with Cercariae Indicae XXX and the other with Cercariae of S. spindalis.
In the former a few schistosomes were found in the sections of the lungs only and
all of them appeared to be males. In some places two worms were met with,
the side of one fitting in the gynecophoral canal of the other. (Fig. 4,
Plate IV, & Fig. 1, Plate V). The latter guinea-pig showed only a few male
S. spindalis in the portal vein and none in the lungs. One white rat was infected
with Cercariae Indicae XXX, it was destroyed after eleven weeks and it failed to
show infection. It is interesting to note that the guinea-pigs showed only
male schistosomes developing in them, though they were infected with portions of
the same material used for infecting the experimental calves in which both males
and females developed. It cannot therefore be considered that the cercariae used
for infecting these small animals may have been unisexual. This supports the
suggestion of Fairley and Mackie [1930], that some host factor in the guinea-pig,
antagonistic to the development of the female schistosomes, underlies the phe-
nomenon of exclusively male survival, rather than initial unisexual infestation.
Though these guinea-pigs had only male worms developing in them, yet the usual
changes were found in the lungs of the one infected with cercariae of nasal
schistosome and in the liver of the other infected with cercariae of S. spindalis.